This invention relates to a butterfly valve and a method for making same.
The butterfly valve typically includes a circular disc member which is pivotally mounted inside a cylindrical bore defining a flow passage. The disc is mounted to turn on an axis extending transversely of the flow passage between an open position where its plane is generally coincident with the direction of flow and a closed position where its plane is at a right angle to the direction of flow. In a closed position a fluid seal is provided either by the outer periphery of the disc sealingly engaging a sealing member provided in the interior of the valve housing or by sealing member carried on the periphery of the disc sealingly engaging a seating surface on the interior of the housing.
Discs used in prior art valves usually are machined or die cast parts. Consequently, butterfly valves have not been widely used in systems requiring a small shutoff valve, e.g., in the 1/2 to 2 inch range, because the relatively massive disc adversely affects the flow characteristics of the valve. Also, machined or die cast discs represent a significant portion of the total fabrication and assembly costs for most butterfly valves.